Insulating Glass
In order to reduce heat gain or loss through glass, two or more
lites may be sealed together to create an insulating glass (IG)
unit.

The majority of
insulating glass units consist of two lites of glass enclosing a
hermetically sealed air space. The lites are held apart by a spacer
around the entire perimeter. The spacer contains a
moisture-adsorbent material called desiccant that serves to keep the
enclosed air free of visible moisture. The entire perimeter of the
assembly is sealed.

The most commonly
used edge construction contains a metallic spacer of roll-formed
aluminum, stainless steel, coated steel or galvanized steel. It is
sealed with a single seal of polysulfide, polyurethane or hot-melt
butyl, or with a dual seal consisting of a primary seal of
polyisobutylene and a secondary seal of silicone, polysulfide or
polyurethane. The corners of the metallic spacer may be square-cut
and joined with a metal, plastic or nylon corner key, may be
miter-cut and brazed, welded or soldered, or may be bent. Recent
years have seen the introduction of warm edge technology products as
spacer materials. These products include extruded butyl materials,
foam rubber based materials, formed plastics and metal strip based
products, many with desiccant included as a component.

Improvements in edge
of insulating glass U-values as a result of warm-edge technologies
play a vital role in meeting overall window performance requirements
for state adopted residential fenestration codes.

Most insulating glass
fabricators voluntarily participate in insulating glass
certification programs. The purpose of the certification programs is
to assure the user that the purchased product is a faithful replica
of one that has passed certain prescribed tests. Therefore,
participants in a certification program must complete the following
requirements: 1) submit specimens of their production product to
independent testing laboratories for the prescribed tests; and 2)
agree to periodic, unannounced inspections of their regular
production by an independent agency to ensure that actual production
employs the same materials and techniques as the tested specimen.

The Insulating
Division of the Glass Association of North America (GANA) and the
Insulating Glass Manufacturers Alliance (IGMA) promote the highest
standards in insulating glass unit production, testing,
certification and business ethics through their memberships. The
industry establishes voluntary quality standards and collects
statistical and other non-proprietary information related to field
performance of insulating glass for dissemination to manufacturers
and consumers.

The above information is from the
GANA Glazing Manual, 2004 Edition - the most frequently
referenced resource in the architectural glass and glazing industry.
The Glazing Manual is an excellent addition to any technical
library.
Go here
to order a copy of the manual or CD-ROM. For further information on
this and other GANA reference documents visit the
PUBLICATIONS section of the GANA website.